1. Field of the Invention
This invention relates to a process for preparing O/W (oil-in-water) rust-inhibiting emulsions based on an oil component, water, at least one emulsifier component, and a corrosion inhibitor. Observing certain conditions in said process leads to especially stable and low viscosity O/W emulsions which ensure good protection from corrosion for metal surfaces made of iron or steel.
2. Statement of Related Art
Rust-inhibiting emulsions are employed for the temporary protection of metallic workpieces from atmospheric influences causing corrosion. Said emulsions substantially contain non-polar or polar oils, emulsifiers, corrosion inhibitors, and water. The effect provided thereby is due to an adsorption of inhibitor molecules on the metal surface and the formation of a protective film from emulsion components, which film acts as a diffusion barrier for the oxygen of the air and for water. Th. Forster et al. in Oberflache-Surface 1989, No. 4, pp. 8-12, report on the mode of action and methods of investigation of rust inhibiting emulsions. Other commercially available systems are based on oil concentrates containing emulsifiers and corrosion inhibitors--but no water. This depends on the emulsifiers and corrosion inhibitors employed being oil soluble. For the preparation of O/W emulsions from such oil concentrates this further means that such systems must be self-emulsifying.
It has been known that oil-in-water emulsions which have been prepared and stabilized with non-ionic emulsifiers can undergo a phase inversion when heated, i.e., at elevated temperatures the outer aqueous phase may become the inner phase. This process, as a rule, is reversible, i.e., upon cooling the initial emulsion type is regenerated. It has also been known that the point of phase inversion temperature is dependent on many factors, e.g., on the kind and phase volume of an oil component, on the hydrophilicity and structure of the emulsifier, and on the composition of the emulsifier system; cf., for example, K. Shinoda and H. Kunieda in Encyclopedia of Emulsion Technology, Vol. I, ed. P. Becher (M. Decker, N.Y., 1983), pp. 337 to 367. It has further been known that emulsions prepared at or slightly below the phase inversion temperature (PIT) are distinguished by particularly fine particle size and particular stability, whereas those emulsions prepared above the phase inversion temperature are less finely divided; cf. S. Friberg, C. Solans, J. Colloid Interface Sci., 66, pp. 367 to 368 (1978). F. Schambil, F. Jost, and M. J. Schwuger, in Progress in Colloid & Polymer Science 73, (1987), pp. 37 to 47, report on the properties of cosmetic emulsions containing fatty alcohols and fatty alcohol polyglycolethers and, in the course thereof, also describe how emulsions produced above the phase inversion temperature exhibit a low viscosity and a high storage stability. In the so far unpublished German Patent Application P 38 19 193.8 by Applicants there has been described a corresponding process for the preparation of stable low-viscosity O/W emulsions of polar oil components.